Electric circuit breaker having an auxiliary switch with an oscillation-damping latch



Oct. 12, 1965 P. BARKAN ETAL 3,211,868

ELECTRIC CIRCUIT BREAKER HAVING AN AUXILIARY SWITCH WITH AN OSCILLATION-DAMPING LATCH Inventors: Philip Barkah, Joh'n A.Oppel,

b9 Ulan 1/m Attorn e5.

Oct. 12, 1965 P. BARKAN ETAL 3,211,858

ELECTRIC CIRCUIT BREAKER HAVING AN AUXILIARY SWITCH WITH AN OSGILLATION-DAMPING LATCH 2 Sheets-Sheet 2 Filed March 14, 1963 Att orneg.

United States Patent O 3,211,868 ELECTRIC CIRCUIT BREAKER HAVING AN AUXILIARY SWITCH WITH AN OSCTLLA- TION-DAMPING LATCH Philip Barkan, Media, and John A. Oppel, Aidan, Pa., assignors to General Electric Company, a corporation of New York Filed Mar. 14, 1963, Ser. No. 265,226 7 Claims. (Cl. 200-146) This invention relates to an electric circuit breaker of the type that is provided with a voltage-controlling impedance shunting its main contacts and auxiliary switching means for interrupting the current owing through the impedance after the main contacts have been opened.

For controlling the voltage developed across the main contacts of a high voltage circuit breaker during a circuit interrupting operation, it has been customary to shunt these contacts with an impedance through which current is transferred when the main contacts are opened to interrupt the circuit. For interrupting the current through the impedance, there is customarily provided an auxiliary switch connected in series with the impedance and in shunt with the main contacts.

In order for the impedance consistently to carry out its intended function during the interrupting process, it is important that the auxiliary switch always be opened at the expiration of a definite predetermined time interval following opening of the main contacts. An arrangement for obtaining this coordination between the main contacts and the auxiliary switch is shown and claimed in U.S. Patent No. 2,91l,546-Oppel, assigned to the assignee of the present invention.

The coordinating arrangement disclosed in the aforesaid patent has performed in a satisfactory manner for most circuit breaker applications, but there are vcertain circuit breaker applications that have exceptionally strin- -gent requirements for precision in the control of this time interval between parting of the main -contacts and parting of the auxiliary contacts. The coordinating arrangement disclosed in this prior patent has had some difliculty in meeting these exceptionally stringent requirements, at least for those operations where the circuit breaker opens immediately after a closing operation.

An object of the present invention is to provide a coordinating arrangement that is capable of controlling this time interval with a high degree of precision even for those opening operations that immediately follow 'a closing operation.

Another object is to provide a latching arrangement for the auxiliary contacts that is capable of causing the contacts that is capable of causing the contacts to be accelerated toward open position upon latch-tripping at a consistent rate for all opening operations, even for those opening operations that immediately follow a closing operation.

One circuit breaker application in which it is important to control the instant of auxiliary-switch opening with great precision is an application in which there are a plurality of these auxiliary switches connected in series in a circuit of very high voltage, e.g., 330 kv. and above. In such an application, it is important that all of the auxiliary switches be opened substantially simultaneously in order to distribute across all of the auxiliary switches the high magnitude recovery voltage developed during interruption lof the impedance current. This becomes especially important when line-charging currents are being switched. If this high magnitude voltage is impressed across only a single auxiliary switch, which may have opened prematurely, it is likely to cause a delayed breakdown, or restrike, across the open auxiliary switch which could lead to the development of excessive over-voltages.

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Obtaining the desired synchronization of the `auxiliary switches is particularly diicult during those Opening operations that immediately follow a closing operation.

Accordingly, another object of our invention is to control the auxiliary contacts of a plurality of series-connected interrupting assemblies in such a manner that their opening operations are synchronized with a high degree of precision, even during those circuit breaker opening operations immediately following a closing -operation.

The requirements for synchronization of the seriesconnected auxiliary switches become evenl more stringent when the circuit breaker is rated for very high speed interrupting performance, for example, two cycles. Another object of our invention is to provide a control for the auxiliary switches that can meet the synchronization requirements imposed by such high speed interrupting ratings, even for those opening operations that immediately follow a closing operation.

In carrying out our invention in one form, we provide separable main contacts, impedance means shunting the main contacts, and separable auxiliary contacts connected in series with the impedance means and in yshunt with the main contacts. A movable one of the auxiliary contacts is biased toward open position by suitable opening means. An actuating member is -coupled to a movable one of the main contacts for transmitting closing force to the movable auxiliary contact when the movable main contact is moved toward closed position. A latch operable when the movable auxiliary contact reaches a closed position is provided for restraining motion of the actuating member in an opening direc-tion under the inuence of the opening means. The latch is controllied by biasing means that moves the latch into a restraining position relative to the actuating member at the instant the actuating member reaches a predetermined point in a closing stroke. The actuating member continues past this predetermined point during a closing operation, and cam means is provided for transmitting a hold-closed force from the latch to the actuating member even when the actuating member is at points past said predetermined point. This cam means -cooperates with the latch to prevent any reverse motion of the actuating member when the actuating member is past said predetermined point and the latch is in its fully-latched position. Means is provided for moving the latch out of restraining relationship with respect to the actuating member at a predetermined point in an opening stroke of the movable main contact so as to permit opening movement of the movable auxiliary contact.

For a better understanding of our invention, reference may be had to the following specication taken in -connection with the accompanying drawings, wherein:

FIG. 1 is a side elevational View, partially in section, showing a circuit breaker embodying one form of our invention. The circuit breaker is depicted in the closed position.

FIG. 2 is a sectional view taken along the line 2 2 of FIG. l.

FIG. 3 is a view similar to that of FIG. 2 except showing the parts of FIG. 2 at an instant during a circuit breaker-opening operation.

FIG. 4 is a view partially in section taken along the line 4 4 of FIG. l.

FIG. 5 is an enlarged detailed view of .a portion of FIG. 3.

FIG. 6 is Ia schematic view illustrating circuit breaking apparatus comprising three series-connected circuit breakers, each corresponding to that illustrated in FIGS. l-5.

Referring now to FIG. 1, the circuit breaker shown therein is of the general type disclosed and claimed in 3 said Patent No. 2,911,546 and in Patent No. 2,783,338- Beatty, both assigned to the `assignee of the present invention. This circuit breaker comprises van enclosed interrupting chamber 11 defined, in part, by a met-allic casing 12 which is filled with pressurized arc-extinguishing gas.

A pair of elongated conductive studs 15 and 20' project into the casing 12 from diametrically-opposed points, and each of these studs carries a suitable stationary contact assembly 16 at its radially inner end. Cooperating with each stationary contact assembly is a movable conta-ct 28 pivotally mounted upon a stationary pivot 29. These pivots 29 are supported upon stationary brackets 31A which are integral with one end of a station-ary operating cylinder 32. Suitable means (not shown are provided for transferring current between the movable contacts 28 and the brackets 31, so that the brackets 31 together with the cylinder 32 form a conductive path electrically interconnecting the two movable contacts 28.

The cylinder 32, at its left hand end, is suitably supported from la generally cylindrical housing 33, which, in turn, is suitably secured at its left hand end to the metallic casing 12. The mechanical connection between the housing 33 and the cas-ing 12 is best shown in FIG. 4, where the housing 33 is .shown provided with a flange 34 that is suitably joined to a flange 35 secured to the casing l12.

For producing a gas-blast action for extinguishing the .arcs which are established by separation of the contacts 16 and 28, the housing 33 is provided with a normallycl-osed annular exhaust passage 36 which leads from the interrupting chamber 11 to the surrounding atmosphere. This will be more readily apparent from FIG. 4. The housing 33 at its ri-ght hand end is formed with a pair of generally diametrically-opposed nozzle-type electrodes 38 defining inlets to the exhaust passage 36. For controlling the lflow of arc-extinguishing gas through the nozzle electrodes 38 and through the exhaust passage 36, there is provided at the cuter end of the exhaust passage 36 a cylind-rically-shaped reciprocable blast valve member 40 which slides smoothly in a surrounding tubular valve housing 41 integrally formed in the housing 33. In FIG. 4, the valve member 40 is shown in its closed position wherein an annular flange 42 formed at its left hand end `sealingly abuts against the stationary ange 34, which serves as a valve seat. The valve member I40 is normally maintained in this closed position of FIG. 4 by the action of a suitable spring (not shown) land by the action of the pressurized gas within the passageway 36 acting upon ange 42.

Since the ch-amber 11 is normally filled with pressurized gas, it will be apparent that when the valve member 40 is opened by movement to the right (by means not shown), gas in the chamber 11 will flow at high speed through the nozzles 38 and out the passage 36 past valve member 40 to atmosphere, as is indicated by the arrows e and 7" shown in FIG. 4. This rapid flow of gas through the nozzles 38 creates an axial arc-enveloping blast whi-ch .acts rapidly to extinguish the arcs which are drawn adjacent the nozzles by movement of the movable contacts 28 away from their stationary contact assemblies 16.

For ope-rating the blast valve 40 and the movable contacts 28, a combined operating mechanism preferably of the fluid-actuated type shown in the aforementioned Beatty patent is provided within the cylinder 32 and 33. The details of this operating mechanism form no part of the present invention and, hence, such details are not shown inthe present application. An adequate understanding of the present invention may be had if it is understood that the operating mechanism acts during an opening operation serves to drive the contacts open. At a predetermined instant after the contacts 28 have been opened, the thenopen blast valve 40 is driven closed by the operating mechanism, as is described in detail in the Beatty patent. This prevents further loss of gas from the interrupting chamber 11.

The means for coupling the piston rod 58 to the main contacts -comprises a crosshead 59 and two sets of connecting links 60. The crosshead 59 is rigidly secured to the piston rod 58 by suitable clamping means, whereas the connecting links 60 are pivotally connected at 61 and `62 to the crosshead and movable contacts, respectively.

In the position of FIG. 1, the movable contacts 28 are biased int-o closed position by means o-f overcenter cornpression springs 64. Each of these springs 64 has one end pivotally supported at 65 on a projecting portion of one of the brackets 31. At their inner ends, the springs 64 are pivotally supported on the crosshead 59. These overcenter springs 64 tend t-o urge the contacts closed while the crosshead 59 is to the left of a reference line connecting the pivots 65. `But when the crosshead is moved to the right beyond this reference line (as occurs during a contact-opening operation), the overcenter springs thereupon tend to urge the contacts in a contactopening direction. This action coupled with that of the operating mechanism acts to hold the contacts A28 in a fullyopen position until the operating mechanism is subsequently operated to close the contacts 28.

Shunting the upper pair of main contacts 16, 28 is an impedance element 70, preferably in the form of a resistor wound about an insulating core 70a carried by a conductive tube 71. The conductive tube 71 is supported from the conductive stud 20 by means of conductive webs 72 electrically interconnecting the tube 71 and the stationary contact assembly 16. The lower terminal of the lresistor 70 is connected to the tube 71, whereas the upper terminal is locally insulated from the tube 71 and is connected by means of a conductor 74 to an electrode 73 of an auxiliary or resistor switch 75.

The auxiliary switch 75 comprises, in addition to the electrode 73, a second electrode 76 spaced from electrode 73 and coacting with electrode 73 to form an interrupting gap between the two electrodes. The electrode 73 is supported on the central housing 33 by an insulator 77 which is capable of electrically isolating the electrode 73 from the housing 33 when the resistor switch is open. The electrode 73 is also supported on the housing 33 but is electrically connected to the housing. Electrically bridging the two stationary electrodes 73 and 76 is a movable electrode 78, which in its closed position of FIG. 1, butts against the two stationary electrodes. Thus, it will be seen that the resistor 70 is connected in shunt with the upper contacts 16, 28 by means of a circuit which extends through the parts 72, 71, 70, 74, 73, 78, 76 and 33. As will be apparent from FIG. l, the lower main contacts 16, 28 are shunted by a similar circuit. Since the parts forming this lower Shunting circuit are substantially identical to those forming the upper circuit, corresponding lower parts have been assigned corresponding reference numerals followed by the suix a.

The electrodes of the resistor or auxiliary switch may be thought of as being auxiliary contacts for the overall circuit breaker and are frequently referred to in the present application as auxiliary contacts.

Referring more particularly to the auxiliary switch 75, it will be noted from FIG. l that each of the movable electrodes 78 and 78a has an elongated pin 80 integral therewith and projecting therefrom to the right. Each of these pins is freely received in an opening formed in a reciprocable cross-beam 81 of insulating material. A pair of compression springs 82 and 82a, each of which is disposed between the cross-beam 81 and one of the movable electrodes 78 or 78a, urges the movable electrodesv into firm circuit-closing engagement with the stationary electrodes. While the switch 75 is in its normal closed position of FIG. 1, the cross-beam 81 is restrained from moving to the right, as will soon appear more clearly. When, however, the cross-beam 81 is driven to the rlght during a switch-opening operation, it eventually impacts against suitable abutments 83 adjustably secured to the outer ends of the pins 80 and 80a and, thus, drives the movable electrodes 78 and 78a to the right into an open position spaced from the stationary electrodes. To aid 1n guiding the cross beam 81 during such openlng movement, a suitable guide pin 84 is shown secured to a stationary poltion of the switch 75 and projecting through a guide opening formed in the crossbeam.

Opening of the auxiliary switch 75 is precisely coordinated with opening of the main contacts 16,.2S by means including a switch-operating rod, or coordinatmg member, 85 which is suitably secured to the crosshead 59, as shown in FIG. l. This secu-ring means of FIG. 1 comprises a pair of nuts 86 threaded on the operating rod 85 and clamping a bracket 87 therebetween. The bracket y87 is bolted or otherwise secured to the crosshead 59.

As will be apparent from FIGS. 1 and 2, the operating rod 85 extends from the crosshead 59, through an opening 89 in the cross-beam 81, into a cylinder 90 mounted :on the casing 33 of the breaker. The opening 89 in the cross-beam 81 is large enough to permit the operating rod 85 to move freely relative to the cross-beam.

As shown in FIG. 2, the operating rod carries at its left hand end an abutment 91 which is preferably threaded thereon and is prevented from accidentally moving out of its position of adjustment by means of a suitable jam nut 92. Further to the right, a second abutment 93 is Secured to the rod 85, and between this second abutment 93 and the cross-beam 81, a compression spring 94 is disposed. This compression spring 94 and the abutment 93 are disposed within a tubular plunger 95, referred to hereinafter as an actuating member, that is secured to the vcrossbeam 81 and is slidably mounted within the cylinder 90 by mean-s yof suitable slide bearing 95a. The compression spring 94 urges the cross-beam 81 to the right toward its -open position, but the cross-beam 81 is restrained in its position of FIG. 2 by the abutment 93. In this regard, as shown in FIG. 2, the abutment 93 bears against an in- 'ternal shoulder of the tubular plunger 95 and, thus, restrains the tubular plunger 95 and hence the cross-beam 81 from moving to the right.

Coacting with the tubular plunger 95 is a latch 96 which is shown pivotally mounted on the cylinder 90 by -a stationary pivot pin 97. The latch 96 at its right hand lend has a head 98 which'is loosely received in a slot 99 formed in the tubular plunger 95. A Irelatively heavy spring, such as the compression spring 100, urges the latch 96 counterclockwise about its pivot 97 into the position of FIG. 2, where its head 98 is seated within the I slot 99.

When the operating rod 85 is driven to the right during a circuit-breaker opening operation, it drives the abutment 93 to the right thereby compressing the spring 94. During such movement of the operating rod 85 from its position of FIG. 2 to that of FIG. 3, the latch 96 blocks movement of the tubular plunger 95 and the connected cross-beam 81, thus preventing the spring 94 from discharging at its right hand end during this interval. As the operating rod continues its rightward opening movement through the position of FIG. 3, the abutment 91 on the `operating rod engages a cam surface 101 formed on the latch 96. This forces the latch 96 downward, thereby releasing it from latching relationship with the tubular plunger 95.

When the latch 96 is so released, the charged spring 94 discharges, thereby forcing the cross-beam 81 to the right. The springs 82 and 82a also discharge in response to latch release and thus aid in driving the cross-beam 81 to the right. The movable contacts 78, 78a remain closed until the cross-beam moves sufliciently to the right to engage the abutments 83, shown in FIG. l. This imvmovement of electrodes 78, 78a.

l beam 81.

pact coupled with continued motion of the cross-beam 81 to the right, simultaneously drives the electrodes 78, 78a to the right into an open-circuit position spaced from the stationary electrodes. Preferably, this opening travel of the electrodes 78 and 78a is approximately equal to the distance moved by the crosshead 59 after the main contacts first part. Thus, at the end opening stroke, the ,shoulder 112 on tubular plunger 95 bears against abutment 93.

The arcs which are established by opening movement of the movable electrodes 78, 78a are quickly extinguished by blasts of uid which flow at high speed through the arcing regions. To this end, the electrodes 76 and 76a are each formed of a hollow construction with centrally disposed blast passages leading into the annular blast pas-sage 36. When the blast valve 40 is opened, pressurized fluid flows at high speed through these blast passages, and the resulting blasts are capable of quickly extinguishing the arcs which are formed by opening When the openin-g operation is completed and the blast valve 40 has closed, the pressurized gas in the interrupting chamber 11 maintans a high dielectric strength insulating gap between Veach pair of spaced contracts, or electrodes, thus maintaining the circuit open.

The above-described operating mechanism for the auxiliary switch 75 is capable of consistently parting the electrodes of the auxiliary switch at the expiration of a precisely-controlled time interval after the main contacts 16, 28 part. In this regard, the operating rod 85 effects release of the latch 96 after the main contacts 16, 28 part and, preferably, near the end of their opening stroke. Even then, the discharging spring 94 does not immediately open the electrodes 78, 78a but must first drive the cross-beam 81 through a preselected lost-motion travel into engagement with the abutments 83 before the switch electrodes 78, 78a begin to part.

With regard to precisely controlling this time-delay with a high degree of consistency, it is to be noted that operation of the switch is not signiiicantly aifected by temperature or pressure variations in the interrupting medium, inasmuch as this medium is not being relied upon as an actuating uid, as in many prior constructions. Nor does the switch rely upon dashpots or similar timers, which are subject to varying characteristics as a result of temperature changes. In the disclosed switch, the point of latch release is controlled positively from the actuating means (59) for the main contacts, and the time-delay occurring thereafter depends to a major extent upon the inertia of the moving parts of the switch 75, since it is such inertia which primarily controls the rate at which the spring 94 drives the contact-actuating cross- It is to be further noted that the electrodes of the auxiliary switch are `of the butt-type substantially devoid of sliding engagement between the electrodes, thus avoiding significant variations in the frictional retarding forces imposed by the contacts during opening movement.

With regard to controlling the time-delay which occurs after the latch 96 is released, the effective mass of the cross-beam 81 is purposely made very large in comparison to that of the contact structure 78, 80, 83 and 78a, 80a, 83a. To this end, a relatively massive block 81a is suitably joined to the cross-beam 81 so as to retard initial discharge of the springs 82 and 94 to a predetermined desired extent. Since the combined mass of the crossbeam together with its attached block is much greater than thatof the contact structure, once the springs 82, 94 have driven these parts 81 and 81a through their lostmotion travel, considerable momentum has been attained and the relatively light contacts 78, 78a can then be picked up without an objectionable reduction in opening speed. This allows the contacts 78 and 78a to open at the desired high speed in spite of the initial retardation of spring discharge.

Closing of the circuit breaker is effected by returning the cross-head 59 from its open position leftward to its closed position shown in FIG. l. At the beginning of this closing stroke, the left end 112 of the tubular casing 95 is bearing against the abutment 93 and, accordingly, initial leftward movement of the crosshead 59 and the connected operating rod forces the tubul-ar casing 95 together with the crossbeam 81 to the left, thus driving the electrodes 78, 78a toward closed po-sition. Simultaneously with such action, leftward movement of thecrosshead 59 is also driving the movable main contacts 28 closed. Since the distance between fully-open position and the point at which the contacts rst touch is approximately the same (in terms of travel of crosshead 59) for both the main contacts and those of the auxiliary switch, the movable contact of each of these sets of contacts first touches its stationary contact at roughly the same instant for each set of contacts.

There are certain circuit breaker applications where the time delay between parting of the main contacts and parting of the auxiliary contacts during an opening operation must be controlled with an exceptional degree of preciseness. One such application is schematically depicted in FIG. 6, where several circuit breakers, or interrupting assemblies, each constructed substantially as shown in FIGS. l-5, are connected in series in a high voltage circuit 120, typically operating at a voltage of 330 kv. or above. The main contacts 28 of all of these assemblies are controlled in a conventional manner to open substantially simultaneously during an opening operation and to close substantially simultaneously during a closing operation. The auxiliary switches 75 of all the assemblies must open substantially simultaneously in order to distribute the high magnitude recovery voltage developed during interruption of the impedance current between all of the auxiliary switches instead of allowing this voltage to concentrate across only a single auxiliary switch. This becomes particularly important when linecharging currents are being switched, and a delayed breakdown, or restrike, across an auxiliary switch 75 can result in transient overvoltages of excessive magnitude. Only a single open auxiliary switch 75 may not have sufficient dielectric strength to prevent such a restrike. But had all the series-connected switches 75 opened before the instant at which this restrike had occurred, then there usually would be sufficient dielectric strength :across the series-connected combination of auxiliary switches to prevent the restrike.

The circuit breaker disclossed in the aforesaid Oppel Patent 2,911,456 has been capable of consistently preventing such restrikes following a straight opening operation of the circuit breaker, i.e., an opening operation following a prolonged closed period. But it has encountered some difficulties in this respect during circuitbreaker opening operations that immediately follow a closing operation, at least when it is one of a plurality of series-connected assemblies in a very high voltage circuit, as shown in FIG. 6. This latter type of opening operation occurs when the circuit breaker is closed on a fault and will be referred to hereinafter as a trip-free opening. In studying this problem, it was found that, during trip-free opening operations, the auxiliary switches 75 of the series-connected assemblies were not opening close enough together in time to distribute the voltage between all of the auxiliary switches. Even though the operations of the series-connected auxiliary switches. 75 were found to be synchronized with sufficient preciseness during a straight opening operation, for some reason, not then understood, this high degree of precision was lacking during a trip-free opening operation.

In further studying this problem, we found that this lack'of precision was resulting from slight oscillations of the plunger 95 at the end of the immediately-preceding closing stroke. These oscillations, which result from rebound of the plunger when its closing motion is terminated, were occurring in a direction parallel to the path of movement of the plunger 95. When an opening stroke was initiated immediately after closing, these oscillations had not yet been completely damped out at the instant the latch 96 for the auxiliary switch 75 was tripped.

The persistence of these oscillations resulted in the plunger 95 having a finite initial velocity, rather unpredictable in magnitude and direction, at the instant of latchtripping. This instantaneous velocity of the plunger 95 :at the instant of the latch-tripping materially affects the Idis-tance that the plunger 95 can move in a given period following latch-tripping. It will therefore be apparent that these initial oscillations can materially affect the time required to open the auxiliary switch 75 following parting of the main contacts 16, 28.

In the auxiliary switch of the present application, we have essentially prevented these oscillations from occurring by providing the plunger 95 with a cam surface 120 that `coacts in a special manner with the latchv 96. The usual latching surface against which a latch, such as 96, bear-s is defined by an arc of a circle havin-g its center coinciding with the axis about which the latch rotates. For example, referring to FIG. 5, such a surface would be defined by the dotted-line arc 122 of a circle having its center coinciding with the axis of pivot pin 97. But our cam surface 120 is shaped so that it purposely does not conform to such -an arc. Its axis of curvature is widely displaced from the axis of pivot 97, and hence the surface 120 may be thought of as being an off-center latching surface. This latching surface 120 is preferably a planar surface disposed at degrees to the longitudinal axis of the plunger and may be also thought of as diverging radially outwardly from the arc 122, considered in the direction moved by the latch 96 as it moves counterclockwise toward its fully-latched position.

During the final portion of a switch-closing operation, the plunger 95 moves through the solid-line position depicted in FIG. 5 into a slightly more advanced fully-closed position depicted in dotted lines. When the plunger enters the solid line position of FIG. 5, the latch 96 is firs-t force-d counterclockwise by its spring 100 into a restraining position behind the latching surface 120, as shown in solid line in FIG. 5. The latch continues moving thereafter in a counterclockwise direction toward a fully-latched position F. As the active surface of latch 96 moves counterclockwise along the arc 1 22 into the dotted-line fully-latched position F, it transmits force to the cam surface 120, and this helps to force the plunger 95 in a closing direction into its dotted-line fully-closed position of FIG. 5. The spring 100 is purposely made strong enough so that once the latch enters the solid-line position of FIG. 5, the spring can drive the latch into its fully latched position F and the plunger 95 into its fully closed position without assistance from other closing forces. In addition, the latch 96 is capable of restraining even slight amounts of reverse movement of plunger 95 from the time the latch enters its initial restraining position of FIG. 5 until it reaches its fully-latched position F. It should be noted that when the latch is in its fully-latched position F andthe plunger 95 is in its fullyclosed dotted line position, there is no clearance between the active surface 125 of the latch and the cam surface 120. Thus, when the plunger 95 is in its dotted-line, fully-closed position and the latch is in its fully-latched position F, even the slightest reverse movement of the plunger is blocked by the latch 96. This is in distinct contrast to the usual latch, where there is a relatively large clearance that must be taken up by reverse moti-on of the plunger (into a position corresponding to the solid line position Iof FIG. 5) before the latch 96 can exert its restraining force on the plunger.

Since the latch 96, when in its fully-latched position F, can block even a slight amount of reverse movement of the plunger 95 from the dotted-line fully-closed position, it will be apparent that when the latch 96 enters its fully-latched position at the end of a closing stroke, it will block any -signiicant reverse motion of the plunger 95 that tends to result from rebound of the plunger at the end of the closing stroke. Thus, the previously mentioned oscillations of the plunger at the end of the closing stroke are substantially prevented. Accordingly, when an opening operation is initiated immediately after closing, the plunger 95 is completely at rest, and not oscillating, when the latch 96 is tripped. This results in a consistent predictable acceleration of the plunger in an opening direction so that upon expiration of a predetermined time, the plunger will have traveled a predetermined amount in an opening direction. This travel is substantially the same whether this opening motion i-s a straight Opening operation or is a trip-free opening operation. This follows from the fact that the plunger 95 is completely at rest immediately preceding an opening operation whether it be a straight opening operation or a tripfree opening operation. This consistent and predictable acceleration .of the movable auxliliary contact 7S enables the other auxiliary switches of FIG. 6 that are connected in series with the above-described auxiliary switch to be synchronized in their opening operation with the abovedescribed auxiliary switch.

Assuming a circuit breaker such as shown in FIG. 6 comprising two or more interrupting assemblies, each constructed as shown in FIG. l, connected in series, it will be apparent that when the auxiliary switches open simultaneously, the recovery voltage will be distributed between all of the auxiliary switches, and the possibility of a restrike will therefore be reduced.

In some cases, it may be desirable or necessary that the plunger 95 have just a slight amount of overtravel, e.g. 17.; inch, beyond the dotted-line, fully-closed position of FIG. 5. This will result in a very slight clearance between cam surface 120 and the latch surface 125 at the very end of the closing stroke. However, by relying upon the latching arrangement of the present invention, this slight clearance can be made so small as to be insignificant from the standpoint of producing oscillations of suiiicient intensity or persistence to affect opening speeds on a trip-free operation. Whether this very slight amount of clearance or zero clearance is present, it will be apparent that any clearance that is present is substantially less than distance traveled by the plunger 95 from its solid line position of FIG. into its dotted-line extreme end position.

In the disclosed circuit breaker, the time delay between parting of the main contacts and parting of the auxiliary contacts must be precisely 'controlled in order to effect synchronized parting of all the auxiliary switches of FIG. 6 since it is the operation of the main contacts that controls the auxiliary switches. However, in its broader aspects, our invention is not limited to an arrangement in which the auxiliary switches are directly controlled by operation of the main contacts. It will be apparent that the latch 96 for each auxiliary switch could be tripped by other means, such as a solenoid or fluid motor, appropriately set into operation at the proper instant after the main contacts parted. In such an arrangement, it is equally desirable that the plunger 96 not be oscillating at the instant latch-tripping begins since such oscillations will introduce inconsistencies in the initial speed of the plunger 95, just as descrbed hereinabove. However, the abovedescribed cooperative relationship between the cam surface 120 and the latch 96 will serve to eliminate these loscillations and facilitate consistent acceleration of the 'plunger 95 upon latch-tripping irrespective of the means ,used for tripping the latch after the main contacts have parted.

While we have shown and described a particular em- -bodiment of our invention, it will be obvious to those claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric circuit breaker of the type that comprises a plurality of circuit interrupting assemblies connected in circuit with each other and simultaneously operable during opening and closing operations of the circuit breaker, each interrupting assembly comprising:

(a) separable main contacts, impedance means shunting said main contacts, separable auxiliary contacts connected in series with said impedance means and in shunt with said main contacts,

(a) opening means for biasing a movable one of said auxiliary contacts toward open position,

(b) an actuating member coupled to a movable one of said main contacts for transmitting closing force to said movable auxiliary contact when said movable main contact is moved toward closed position,

(b') spring means through which closing force is transmitted between said actuating member and said movable auxiliary contact,

(c) a latch operable-when said movable auxiliary contact reaches a closed position for restraining movernent of said actuating member in an opening direction under the iniluence of said opening means,

(d) biasing means for moving said latch into a restraining position relative to said actuating member at the instant said actuating member reaches a predetermined point in a closing stroke,

(e) said actuating member continuing past said predetermined point in moving through a closing stroke,

(f) cam means for transmitting a hold-closed force from said latch to said actuating means when said actuating means is located at points along a substantial portion of its travel past said predetermined point, considered in a closing direction,

(g) and means operable during a circuit breaker opening operation for moving said latch out of restraining relationship with respect to said actuating member at a predetermined instant after said main contacts part to permit opening motion of said movable auxiliary contact,

(h) said hold-closed force rapidly damping oscillations of said actuating member at the end of a closing operation, whereby, during an opening operation of said circuit breaker immediately following closing thereoef, said actuating member is substantially at rest when said latch is moved out of said restraining relationship, thus substantially eliminating interference from said oscillations on synchronization of the opening of the movable auxiliary contacts of said interrupting assemblies.

2. In an electric circuit breaker of the type that comprises a plurality of circuit interrupting assemblies connected in circuit with each other and simultaneously operable during opening and closing operations of the circuit breaker, each interrupting assembly comprising:

(a) separable main contacts, impedance means shunting said main contacts, separable auxiliary contacts connected in series with said impedance means and in shunt with said main contacts,

(a) opening means for biasing a movable one of said auxiliary contacts toward open position,

(b) an actuating member coupled to a movable one of said main contacts for transmitting closing force to said movable auxiliary Contact when said movable main contact is moved toward closed position,

(b') spring means through which closing force is transmitted between said actuating member and said movable auxiliary contact,

(c) a latch operable when said movable auxiliary contact reaches a closed position for restraining movement of said actuating member in an opening direction under the inliuence of said opening means,

(d) biasing means for moving said latch into a restraining position relative to said actuating member at the instant said actuating member reaches a predetermined point in a closing stroke,

(e) said actuating member continuing past said predetermined point in moving through a closing stroke,

(f) cam means for rendering said latch capable of opposing reverse motion of said actuating member when said actuating member is at points along a substantial portion of the closing stroke travel past said predetermined point whereby to limitsuch reverse movement at the end of a closing stroke,

(g) and means for operable during a circuit breaker opening operation for moving said latch out of restraining relationship with respect to said actuating member at a predetermined instant after said main contacts part to permit opening motion of said movable auxiliary contact,

(h) said opposition of reverse motion rapidly damping oscillations of said actuating member at the end of a closing operation, whereby, during an opening operation of said circuit breaker immediately following closing thereof, said actuating member is substantially at rest when said latch is moved out of said restraining relationship, thus substantially eliminating intereference from said oscillations on synchronization of the opening of the movable auxiliary contacts of said interrupting assemblies.

3. In an electric circuit breaker of the type that cornprises a plurality of circuit interrupting assemblies connected in circuit with each other and simultaneously operable during opening and closing operations of the circuit breaker, each interrupting assembly comprising:

(a) separable main contacts, impedance means shunting said main contacts, separable auxiliary contacts connected in series with said impedance means and in shunt with said main contacts,

(a) opening means for biasing a movable one of said auxiliary contacts toward open position,

(b) an actuating member coupled to a movable one of said main contacts for transmitting closing force to said movable auxiliary Contact when said movable main contact is moved toward closed position,

(b) spring means through which closing force is transmitted between said actuating member and said movable auxiliary contact,

(c) a latch operable when said movable auxiliary contact reaches a closed position for restraining movement of said actuating member in an opening direction under the iniiuence of said opening means,

(d) biasing means for moving sail latch into a restraining position relative to said actuating member at the instant said actuating member reaches a predetermined point in a closing stroke,

(e) the closing stroke of said actuating member continuing past said predetermined point for a predetermined distance to permit said biasing means to drive said latch into a fully-latched position when said actuating means is at the end of its closing stroke,

(f) cam means fixed to said actuating member for transmitting a hold-closed force from said latch to said actuating member when said actuating member is located at points along a substantial portion of said closing stroke travel past said predetermined point,

(g) said cam means being so shaped that any clearancebetween said cam means and said latch when said latch is in its fully-latched position is substantially less than said predetermined distance,

(h) and means operable during a circuit breaker opening operation for moving said latch out of restraining relationship with respect to said actuating member at a predetermined instant after said main contacts have parted to permit opening movement of said movable auxiliary contact,

(i) said hold-closed force rapidly damping oscillations of said actuating member at the end of a closing operation, whereby, during an opening operation of said circuit breaker immediately following closing therof, said actuating member is substantially at rest when said latch is moved out of said restraining relationship, thus substantially eliminating interference from said oscillations on lsynchronization of the opening of the movable auxiliary contacts of said interrupting assemblies.

4. The combination of claim 3 in which said latch moves toward its fully-latched position along an arcuate path about a predetermined pivot axis, and said cam means comprises a cam surface engaged by said latch that diverges radially outwardly from said arcuate path relative to said axis, considered in the direction of latch movement toward the fully-latched position.

5. In a circuit interrupting assembly of the type that comprises a plurality of circuit interrupting assemblies connected in circuit with each other and simultaneously operable during opening and closing operations of the circuit breaker, each interrupting assembly comprising:

(a) separable main contacts, impedance means shunting said main contacts, separable auxiliary contacts connected in series with said impedance means and in shunt with said main contacts,

(a) opening means for biasing a movable one of said auxiliary contacts toward open position,

(b) means for moving said movable auxiliary Contact toward closed position during a closing operation of said circuit breaker,

(b) spring means through which closing force is transmitted between said force-transmitting member and said movable auxiliary contact,

(c) a force-transmitting member coupled to said movable auxiliary contact,

(d) a latch operable when said movable auxiliary contact reaches a closed position for restraining movement of said force-transmitting member in an opening direction under the influence of said opening means,

(e) biasing m-eans for moving said latch into a restraining position relative to said force-transmitting member at the instant said force-transmitting member reaches a predetermined point in a closing stroke,

(f) said force-transmitting member continuing past said predetermined point in moving through a closing stroke, f

(g) cam means for rendering said latch capable of opposing reverse motion for said force-transmitting member when said force-transmitting member is at p points along a substantial portion of the closing stroke travel past said predetermined point whereby to limit such reverse movement at the end of a closing stroke,

(h) and means operable during a circuit breaker opening operation for moving said latch out of restraining relationship with respect to said force-transmitting member at a predetermined instant after said main contacts part to permit opening motion of said movable auxiliary Contact,

(i) said opposition of reverse motion rapidly damping oscillations of said force-transmitting member at the end of a closing operation, whereby during an opening operation of said circuit breaker immediately following closing thereof, said force-transmitting member is substantially at rest when said latch is moved out of said restraining relationship, thus substantially eliminating interference from said oscillations on synchronization of the opening of the movv able auxiliary contacts of said interrupting assemblies.

6. The combination of claim 5 in which said latch has a fully-latched position toward which it is moved by said biasing means when said force-transmitting member reaches said predetermined point in a closing stroke,

3,211,868 13 e 14 said latch moving from itsinitial restraining position tQ References Cited by the Examiner said fully-latched position along an arcuate path about a UNITED STATES PATENTS predetermined pivot axis, and said cam means comprising tion toward said fully-latched position. KATHLEEN H CLAFFY Primary Exammer 7. The electric circuit breaker of claim 5 in which said ROBERT K. SCHAEFER, BERNARD A. GILHEANY, interrupting assemblies are electrically connected in series. 10 Examiners. 

1. IN AN ELECTRIC CIRCUIT BREAKER OF THE TYPE THAT COMPRISES A PLURALITY OF CIRCUIT INTERRUPTING ASSEMBLIES CONNECTED CIRCUIT WITH EACH OTHER AND SIMULTANEOUSLY OPERABLE DURING OPENING AND CLOSING OPERATIONS OF THE CIRCUIT BREAKER, EACH INTERRUPTING ASSEMBLY COMPRISING: (A) SEPARABLE MAIN CONTACTS, IMPEDANCE MEANS SHUNTING SAID MAIN CONTACTS, SEPARABLE AUXILIARY CONTACTS CONNECTED IN SERIES WITH SAID IMPEDANCE MEANS AND IN SHUNT WITH SAID MAIN CONTACTS, (A'') OPENING MEANS FOR BIASING A MOVABLE ONE OF SAID AUXILIARY CONTACTS TOWARD OPEN POSITION, (B) AN ACTUATING MEMBER COUPLED TO A MOVABLE ONE OF SAID MAIN CONTACTS FOR TRANSMITTING CLOSING FOR SAID MOVABLE AUXILIARY CONTACT WHEN SAID MOVABLE MAIN CONTACT IS MOVED TOWARD CLOSED POSITION, (B'') SPRING MEANS THROUGH WHICH CLOSING FORCE IS TRANSMITTED BETWEEN SAID ACTUATING MEMBER AND SAID MOVABLE AUXILIARY CONTACT, (C) A LATCH OPERABLE WHEN SAID MOVABLE AUXILIARY CONTACT REACHES A CLOSED POSITION FOR RESTRAINING MOVEMENT OF SAID ACTUATING MEMBER IN AN OPENING DIRECTION UNDER THE INFLUENCE OF SAID OPENING MEANS, (D) BIASING MEANS FOR MOVING SAID LATCH INTO A RESTRAINING POSITION RELATIVE TO SAID ACTUATING MEMBER AT THE INSTANT SAID ACTUATING MEMBER REACHES A PREDETERMINED POINT IN A CLOSING STROKE, (E) SAID ACTUATING MEMBER CONTINUING PAST SAID PREDETERMINED POINT IN MOVING THROUGH A CLOSING STROKE, (F) CAM MEANS FOR TRANSMITTING A HOLD-CLOSED FORCE FROM SAID LATCH TO SAID ACTUATING MEANS WHEN SAID ACTUATING MEANS IS LOCATED AT POINTS ALONG A SUBSTANTIAL PORTION OF ITS TRAVEL PAST SAID PREDETERMINED POINT, CONSIDERED IN A CLOSING DIRECTION, (G) AND MEANS OPERABLE DURING A CIRCUIT BREAKER OPENING OPERATION FOR MOVING SAID LATCH OUT OF RESTRICTING RELATIONSHIP WITH RESPECT TO SAID ACTUATING MEMBER AT A PREDETERMINED INSTANT AFTER SAID MAIN CONTACTS PART TO PERMIT OPENING MOTION OF SAID MOVABLE AUXILIARY CONTACT, (H) SAID HOLD-CLOSED FORCE RAPIDLY DAMPING OSCILLATIONS OF SAID ACTUATING MEMBER AT THE END OF A CLOSING OPERATION, WHEREBY, DURING AN OPENING OPERATION OF SAID CIRCUIT BREAKER IMMEDIATELY FOLLOWING CLOSING THEREOF, SAID ACTUATING MEMBER IS SUBSTANTIALLY AT REST WHEN SAID LATCH IS MOVED OUT OF SAID RESTRAINING RELATIONSHIP, THUS SUBSTANTIALLY ELIMINATING INTEREFERENCE FROM SAID OSCILLATIONS ON SYNCHRONIZATION OF THE OPENING OF THE MOVABLE AUXILIARY CONTACTS OF SAID INTERRUPTING ASSEMBLIES. 